Field
The present disclosure relates to medical devices, systems and methods for accessing cranial and intracranial structures. Specifically, the disclosure is directed to altering brain function and treating cranial and intracranial pathology. More specifically, the disclosure is directed to the surgical implantation of electrodes or other devices towards, within or through the cranium to alter or improve brain function and pathological states such as stroke, seizure, degeneration, and brain tumors. Most specifically, the disclosure is directed to minimizing surgical methods and risks and maximizing the length of devices that can be implanted towards, within or through the cranium and their ability to hold charge. Further most specifically, the disclosure maximizes the access to intracranial elements through minimally invasive portals in the skin, scalp, or cranium.
Description of the Related Art
Electrical stimulation of the brain can improve and ameliorate many neurologic conditions. Examples of the success of brain stimulation include deep brain stimulation for Parkinson's Disease, tremor, dystonia, other movement disorders, epilepsy, and pain. Additionally, potential new sites of deep brain stimulation demonstrate promising results for other conditions such as obesity, depression, psychiatric disorders, memory, migraine headache, and minimally conscious states.
Deep brain stimulation involves placing a long electrode through a burrhole in the cranium to a target deep to the surface of the brain. The electrode is placed under stereotactic guidance which is performed with or without a frame. Frame based systems such as the Leksell or CRW frame require that a rigid stereotactic frame is clamped to the skull through a number of screws that are fixed to the cranium. Frameless systems utilize fiducial markers placed on the skin. In both methods, an MRI (magnetic resonance imaging) or CT (computed tomography) scan is performed with the frame or fiducial markers in place. In frame based stereotaxy, computer assisted reconstruction of the brain and target area is performed to localize the target in relation to the coordinates of the frame. In frameless stereotaxy, a three-dimensional reconstruction of the cranium and brain is matched to the three-dimensional configuration of the fiducial markers or anatomical landmarks. The end result in both cases is the ability to place electrodes accurately into virtually any part of the brain.
The cerebral cortex is another structure that yields a large potential for therapeutic intervention. In deep brain stimulation, the electrode passes through the cerebral cortex as well as subcortical brain structures to reach the affected deep brain nuclei and therefore risks injury to the intervening healthy brain tissues as well as blood vessels. These unnecessary yet unavoidable injuries can potentially result in loss of brain functions, stroke, and intracranial hemorrhage. On the other hand, stimulation of the cerebral cortex is safer because electrodes are placed on the surface of the brain or even outside the covering of the brain, i.e. dura mater, a technique called epidural electrode stimulation. Additionally most of the subcortical or deep brain structures have connections with known targets in the cortex, making these targets candidates for cortical stimulation. Accordingly, directly stimulating the cortex can affect subcortical and deep brain structures that directly or indirectly communicate with the cortical targets. Previous studies have demonstrated success in using cortical stimulation for the treatment of epilepsy, stroke rehabilitation, pain, depression, and blindness.
In addition to the treatment of pathologic conditions, brain stimulation and recording provides the virtually unlimited potential of augmenting or improving brain function. These technologies allow the brain to bypass dysfunctional neural elements such as due to spinal cord injury, amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis (MS), and blindness. Brain recording and stimulation techniques in these cases provide a bridge for neural signals to cross injured or dysfunctional elements both on the input as well as the output side. For example in the case of ALS or a patient with locked-in syndrome, the patient is awake and conscious but without any ability to interact with the environment. These patients are essentially trapped within their brain. Recently, it has been demonstrated that by placing recording electrodes directly on the surface of the brain, these patients can learn to control computer cursors and other devices through their own brainwaves. This method of direct control of external devices through brainwaves is called brain-machine interface.
Brain-machine interface has also been implemented using brainwaves recorded outside the cranium—electroencephalography (EEG), which detects the neural signals passing through the cranium with electrodes placed on the scalp. Although noninvasive, brain-machine interface using EEG signals is currently limited from the significant dampening of the brainwave's amplitude by the cranium and interference by muscles in the scalp and head. Only the largest potentials among the brain signals are detectable by the EEG approach. The best and most robust recording of brainwaves utilize electrodes implanted inside brain tissue or on the surface of the brain (electrocorticography) either in the subdural or epidural spaces. These intracranial signals have been shown to be more robust, better localized and are more effective for the use of brain-computer interface technology.
Similarly the cortex and some subcortical fibers can be activated through the cranium by transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS). In this approach, magnetic waves (TMS) or electrical currents (tDCS) are activated on the scalp outside the cranium and transmitted through the cranium to activate parts of the cortex and subcortical fibers. TMS has been effective in treating a number of disorders such as depression, migraines, and movement disorders. Additionally some reports suggest that TMS may be able to boost memory and concentration. Similarly tDCS appears to improve some forms of learning when applied in low doses. This evidence suggests that stimulation of the cortex may have a large, virtually unlimited, variety of applications for treating central nervous system pathology as well as enhancing normal brain functions.
Electrical stimulation has also been applied effectively for the treatment of certain tumors. By applying an electrical field that disrupts the physiology of tumor cells, tumors have been found to shrink. Tumors in the brain, particularly those close to the surface of the brain such as meningiomas may also be treated by electrical stimulation. In addition to electrical fields, heat (thermoablation) and cold (cryoablation) have also demonstrated effectiveness towards tumors. Focused ultrasound has also been used to both modulate as well as destroy intracranial targets such as tumors as well as normal and pathologic brain areas (seizure foci, tremor generators, movement disorder generators, depression generators, overactive areas, underactive areas, etc. . . . ).
Prior art and current state of the art for brain stimulation technologies require the placement of electrodes either through a craniotomy where a flap of the skull is removed and then replaced, or a bun hole where a small hole is drilled in the skull and the brain can be visualized. These procedures necessitate a minimum of an overnight stay in the hospital and pose risk to injury of the brain due to the invasiveness of the techniques. Additionally these “open” techniques pose special challenges for securing the electrode as most technologies require a lead to exit the hole in the skull. Unless these electrodes are tethered by a suture or device, there is possibility of migration or movement, particularly in the context of continuous pulsatile movement of the brain in relation to the skull.
Current techniques for cortical stimulation also risk the development of scarring of the cortex as well as hemorrhage. With long term placement of foreign objects on the brain or spine, scarring (gliosis and inflammation) occurs. This is seen with both spinal cord stimulators placed on the spinal cord as well as prostheses placed on the surface of the brain. Scarring distorts the normal brain architecture and may lead to complications such as seizures. Additionally, the placement of devices on the surface of the brain poses risks of hemorrhage. A previous clinical case illustrates the dangers: a patient who received subdural cortical electrode implantation suffered significant intracranial hemorrhage after suffering head trauma. Thus in the case of a deceleration injury like that seen in traffic accidents or falls, the imperfect anchoring of the electrode and the mass of the electrode may cause the electrodes to detach and injure the brain. Blood vessels also can be sheared from the sudden relative movement of the electrode on the brain, leading to subdural, subarachnoid, and cortical hematomas. However, if the electrodes were embedded within the skull then there is no risk of this type of shearing injury during traumatic brain injury such as from sudden impact accidents.
In order to expand the indications of brain stimulation to a larger population of patients, the invasiveness of techniques for placement of the electrodes needs to be minimized. As many surgical specialties have demonstrated, minimized surgical approaches often translate into safer surgeries with shorter hospital stays and greater patient satisfaction.
Recent advances in the miniaturization of microelectronics have allowed the development of small, completely contained electrode systems, called the bion, that are small enough to be injected into muscle and other body parts through a hypodermic needle. This type of microelectrode device contains stimulation and recording electrodes, amplifier, communication, and power components all integrated into a hermetically sealed capsule. While some bion devices have batteries integrated with the unit, others are powered by radiofrequency transmission. Although muscle and other body parts allow the implantation of bion electrodes, the cranium poses a challenge to the bion because the cranium is roughly 1 cm or less in thickness. This finite thickness limits the size of the electronic components as well as the size of the battery. Battery capacity (the amount of energy stored within the battery) determines the length of time between charges in a rechargeable battery and is effected by the length of the battery. In the case of the bion, an injectable device that demands a small diameter, the battery capacity is directly related to the length of the battery. A longer bion electrode permits a longer battery and hence greater battery capacity and a longer run time without recharging.
Some patents exist covering implantable stimulators and electrical stimulation therapy systems. However, these patents are not specially adapted for insertion through the skull with multiple components through a single site by means of introducing some components at non-orthogonal angles.
For example, U.S. Pat. No. 5,324,316 entitled “Implantable microstimulator” by Joseph H. Schulman, et al. and assigned to the Alfred E. Mann Foundation For Scientific Research (Sylmar, Calif.) discloses an implantable stimulator with electrodes inside a hermetically-sealed housing that is inert to body fluids. The electrodes receive energy from a capacitor that stores energy and includes a coil transformer which, in turn, receives energy from an alternating magnetic field. The patent discloses “[t]he microstimulators, of course, may be planted in or near any part of the body, in the brain, a muscle, nerve, organ or other body area” (See 4:24-26) However, no details are provided on how the microstimulators would be or could be implanted into the brain. The presumption would be that this is done according to conventional ways such as by introducing traditional long electrodes through burr holes. There is no mention of insertion through the skull or cranium. The patent emphasizes the stimulators are implanted by “expulsion through a hypodermic needle” (Abstract, 1:13-15, 2:7-10, 2:35-37, etc.). Certainly a hypodermic needle cannot be injected through the skull which suggests these stimulators are not designed for such a purpose. Further, there is no disclosure of multiple interconnected components through a single entry site by insertion of some components at non-orthogonal or diagonal angles. The hermetically sealed housing inert to body fluids would prevent the microstimulators from hard-wired communication with one another and from sharing power through hard-wired connections with other units. Thus, in the system of USP '316 each microstimulator is essentially its own physically isolated entity interacting with and charged by an external magnetic field but not interacting with the other microstimulators except through wireless communication.
U.S. Pat. No. 6,208,894 entitled “System of implantable devices for monitoring and/or affecting body parameters” also by Joseph H. Schulman, et al. and also assigned to the Alfred E. Mann Foundation For Scientific Research (Sylmar, Calif.), as well as Advanced Bionics, Inc., discloses a system control unit (SCU) and one or more other devices designed to be “implanted in the patient's body, i.e., within the envelope defined by the patient's skin” rather than through the skin and/or through the skull. In the present disclosure the skull rather than the skin defines the envelope. The SCU wirelessly communicates with the various addressable devices and in some cases the addressable devices wirelessly communicate with one another (7:50). In the present disclosure, the interconnection of multiple devices at the insertion point permits several devices to communicate directly (even in the absence of an intermediary SCU) and through direct contact (which may be more reliable than wireless). USP '894 does not refer to the skull or cranium. USP '894 refers to sensing signals originating from or generated by a patient's brain (2:44-48, 11:3-6) but does not disclose that any of the devices are actually inserted into the brain or on its surface (epidurally). Rather, it appears the devices are implanted past sites of nerve damage and used to replace damaged nerves (2:40-52).
Advanced Bionics, Inc. has several of its own microstimulator “system” patents. For example, see U.S. Pat. No. 6,181,965; U.S. Pat. No. 6,175,764; and U.S. Pat. No. 6,051,017. These patents also disclose implantable microstimulator systems with hermetically sealed housings and configured for implantation through a hollow cannula. The electrodes protrude from the housing. Additionally, the housing has a polymeric coating that may contain a chemical or pharmaceutical agent for providing drug therapy simultaneous with electrical stimulation. There is no mention of the skull or cranium and the brain is referred to only in the background discussion with respect to the communication of signals from the brain and loss of voluntary muscle function from injury to the brain.
Advanced Bionics, Inc. also has various other “method” patents that specifically refer to brain stimulation through the implantation of a system control unit and electrode in the brain (see for example, U.S. Pat. No. 7,151,961; U.S. Pat. No. 7,013,177; and U.S. Pat. No. 7,003,352.) These patents emphasize method claims. The implantable microstimulator SCU/electrode systems disclosed therein are similar and the methods apply to the many applications for such systems. The methods require the control unit to be implanted “entirely within the brain” (vs. on the surface or external to the body) (see USP '961 claim 1 and USP '177 claim 28) and emphasize drug delivery from a pump and infusion outlet coupled with or as an alternative to electrical stimulation. The patents do refer to the “skull” in the context of “implanting . . . in at least one of the skull and the brain” (see USP '177 claims 1, 14, 19, 23). There is no disclosure of multiple components through a single entry site or non-orthogonal/diagonal/radial angles of insertion.
Vertis Neuroscience, Inc. has two patents that discuss insertion angle control and depth control of an electrode. However, neither patent teaches or suggests incorporating the electrode in a screw housing or other component capable of penetrating the skull or cranium (rather than just the skin) for access to the brain's cortex. There is no teaching of applying angle and depth control in order to fit more than one electrode through a single entry site. FIG. 10-11 show multiple entry sites with a separate spot for each electrode.
U.S. Pat. No. 6,622,051 entitled “Percutaneous electrical therapy system with electrode entry angle control” by Jon M. Bishay, et al. discloses an electrode with a sharp tip and a device for controlling the angle of entry of the electrode through tissue. There is no mention of non-orthogonal or diagonal angles of insertion in order to fit more electrodes or other components through the same entry site. The angle of entry control assembly is used to control where the sharp point on the tip of the electrode will ultimately end up in order to refine localized electrical stimulation therapy. The electrodes are dispensed from an introducer with springs similar to the expulsion methods through needles and cannulas as disclosed in the Alfred Mann and Advanced Bionics patents. Multiple electrodes may be arranged radially about a hub and dispensed from the same introducer (10:17-27). However, there is no disclosure of inserting multiple electrodes through the same entry site. The introducer could be moved to insert the various electrodes in different chambers at different locations.
U.S. Pat. No. 6,549,810 entitled “Percutaneous electrical therapy system with electrode depth control” by Paul Leonard, et al. is similar to USP '051 but also uses a depth control assembly to direct positioning of the sharp tip of the electrode within tissue, in addition to the angle control assembly. The depth control assembly includes an actuator and a limit stop. In the present disclosure the length of the electrode can be used to determine its optimal angle of insertion so that electrode length equals length through the skull. This permits the electrode to just exit the skull and terminate at the brain's cortex, balancing maximum effectiveness with minimal invasiveness. Thus, electrode length is fixed and taken into account to determine the angle so that when the electrode is inserted (an actuator not being necessary to do this) it can be inserted all the way without need for a limit stop.
In both Vertis patents the electrode communicates electrically with a transmitting control unit. There is no disclosure of the electrodes themselves being used to transmit.
NeuroPace, Inc. has patents (i.e. U.S. Pat. No. 6,016,449) on implantable systems where the control module is placed in the cranium but requiring either additional burr holes or openings in the cranium for the stimulating electrodes to enter the cranium. These designs are significantly more invasive than having just one opening in the cranium and continue to carry the risk of electrodes moving with respect to the brain during head injuries.
In the present disclosure an electrode can communicate with and work together with other electrodes and supporting components (i.e. receivers, transmitters, batteries, rechargers, etc.) for an integrated therapy system with multiple components insertable through the same site.